Flame photometer using photovoltaic cell having logarithmic response



Sept. 1; 1970 o w. DUMPLETON 3,526,770

FLAME PHOTOM ETER USING PHOTOVOLTAIC CELL .Filed 001;. 28, 1966 HAVING LOGARITHMIC RESPONSE 2 Sheets-Sheet 1 INVENTOR Owen W. Dumpleron ATTORNEY Sept 19-70 0. w. DUMPLETON v 3,526,770

FLAME PHOTOMETER USING PHOTOVOLTAIC CELL HAVING LIOGARITHMIG RESPONSE 2 Sheets-Sheet 2 Filed Oct. 28, 1966 5 9 3 NJ 5 ms \mm 5 a: m: H mm 3 E w J 3: h: u u 3 9Q \W N3. 5 2i m8 5 n m: a: w: QN mm .H. :1 2m mQ N12 A 1 @Q m: w: Q8 m9 Na F3 m: 7 llllll IIL mm \QHHI w: A is? N a K a: m9 m2 United States Patent 3,526,770 FLAME PHOTOMETER USING PHOTOVOLTAHC CELL HAVING LOGARITHMIC RESPONSE Owen W. Dumpleton, North Harrow, Middlesex, England, assignor to Babcock & Wilcox Limited, London,

England, a corporation of Great Britain Filed Oct. 28, 1966, Ser. No. 590,295 Int. Cl. H011 15/02 US. Cl. 250-217 Claims ABSTRACT OF THE DISCLOSURE An arrangement of apparatus for monitoring a flame from a burner is provided in which a photovoltaic device having a logarithmic response characteristic is utilized in conjunction with an electrical circuit to obtain an output representative of the ratio of flame radiation flicker to average flame radiation.

Flame monitoring apparatus is useful in connection, for example, with water tube boiler furnaces having a plurality of burners and in such application radiation responsive means in the form of photo-conductive cells may be placed at the outer ends of sighting tubes in line with the flame fronts of the burners and connected in electronic circuits so that the photo-cells, responding to radiations from the burner flames, may cause actuation of desired indicating and/ or alarm and/ or control means, as for example, means to sound an alarm and to cut off fuel supply to a burner if combustion at the burner becomes unsatisfactory. Since an efficient or healthy flame at a burner tends to produce a characteristic flicker or high frequency fluctuation, the radiation therefrom which is absent or not present to the same degree if the combustion at the burner is ineflicient, the flicker response of the cell is useful for monitoring. As pointed out in British Pats. Nos. 962,800, 976,621 and 976,622, it is advantageous to compare the flicker component of thecell radiation with the average radiation of the cell since thereby healthy combustion may be detected even if the cell flicker responses are weakened by causes such as possible deposits on sight glasses of the sighting tube and in those patents means are described for making comparisons between the flicker component of the radiation and the average radiation of certain photo-conductive cells and electronic circuits yielding outputs representative of such comparisons.

The present invention is based on the appreciation that the derivation of a circuit output which is representative of the ratio of flame radiation flicker to average flame radiation may be facilitated by the proper exploitation of a photo-cell to receive the radiations which has certain suitable characteristics. According to the invention, in apparatus for monitoring a flame from a burner, including radiation responsive means arranged to receive flame radiation and connected in an electronic circuit adapted to provide an output representative of the ratio of flame radiation flicker to average flame radiation, the radiation responsive means is a photovoltaic device arranged so that the generated thereacross is proportional or substantially so to the logarithm of the illumination thereof by flame radiation and the fluctuations thereacross are detected to provide the desired output.

A suitable photovoltaic device may be a silicon photovoltaic cell having the characteristic that when operated at constant current therethrough or at a very low current therethrough the thereacross in volts (v) is proportional to the logarithm of the radiation at the cell measured in lumens per square foot (L), i.e. v is proportional to log L. This equation can lead to the differential equation that dv is proportional to dL/L, which may be physically interpreted as a statement that a measurement of voltage fluctuations across the cell having an amplitude equal to dv gives a measure of the ratio of radiation fluctuations of amplitude dL at the cell to the average radiation L at the cell. Thus if the said ratio remains the same because the combustion efliciency at a burner monitored by apparatus properly using said cell remains high the measurement of voltage fluctuations across the cell will remain constant in spite of the depositing of dust on sight glasses or other causes reducing the transmission of radiation from the flame to the cell.

It will be understood that the formation of an output representative of the ratio of flame radiation flicker to average flame radiation and suitable to cause actuation of desired indicating and/ or alarm and/or control means when the appropriate conditions arise may require the amplification of voltage fluctuations across the cell arising from flame flicker and may require the rectification of the amplified fluctuations.

Suitably the flame monitoring apparatus when applied to monitoring the flame of a burner of a water tube boiler furnace provides not only a signal representative of the ratio of flame radiation flicker to average flame radiation but an additional signal derived from the cell response and representative of the average radiation at the cell, which signal may be used for additional indicating and/or alarm and/or control purposes. Thus the value of said additional signal may be such as to denote unserviceability of the flame monitoring apparatus by reason of excessive deposits on sight glasses between the flame and the cell, or, if it is known that the apparatus is serviceable, may denote that the flame is extinguished. The additional signal, instead of or in addition to being used for the said indicating and/ or alarm and/or control purposes may be used to interrupt the passage of the first signal, whereby indicating devices, for example, to which the first signal passes, may not falsely show efficient combustion at a burner not in operation, which it might otherwise do if the cell responds to radiation reflected by some surface from another burner in operation in the same furnace.

The invention will now be described by way of example with reference to the accompanying drawings in which:

FIG. 1 is a sectional side elevation of a pulverized coal burner arranged at a combustion chamber firing port and having an oil burner arranged coaxially thereof; and

FIG. 2 is a circuit diagram of an electrical network for generating output signals in dependence upon fluctuating burner flame illumination of a silicon photovoltaic ce 1.

Referring to FIG. 1 of the drawings, a pulverized coal burner 1 and an oil lighting-up and auxiliary burner 2 are arranged for discharge of respective fuels at a firing port 3 in a water-cooled side wall 4 of a combustion chamber 5. The pulverized coal burner 1 is of the kind which tends to give a flame surrounding a space or hollow core near the burner and about the axis and in which pulverized coal entrained by a stream of primary combustion air is conducted to the firing port in a pipe 6 which extends axially of the firing port; the pipe 6 extends through a windbox 7 on the outer side of the combustion chamber wall 4, and the pulverized coal and primary air shortly after leaving the open end 8 of the pipe 6 impinge upon a pulverized fuel burner vaned diffuser or impeller 9 which is arranged at the throat or narrowest part 10 of the firing port 3 and which is adapted to give radially outwardly directed components of motion to pulverized coal particles as well as to promote mixing between the primary air and secondary combustion air that flows through the throat around the diffuser 9 and comes from the windbox 7. The secondary air is admitted to the throat under control of an air register 11 comprising an annular row of rotatable vanes 12 which can be closed upon one another to an adjustable extent to vary the air through-flow area.

The pulverized coal and primary air are supplied to the burner by a vertical conduit 13 outside the windbox 7 and through an elbow piece 14 secured at one end to the pipe 6 and at the other end to the conduit 13. The diffuser 9 is secured at the inner end of a tubular member 15 which extends axially of the port within the pipe 6 and through an aperture 16 in a cover plate 17 of the elbow piece 13. Supported within the tubular member 15 and extending longitudinally thereof and outwardly beyond the tubular member is the barrel 21 of the oil burner 2, which is pressure-atomizing and which comprises an atomizer head 23 secured in relation to the inner end of the barrel 21 and a burner tail piece 24 to which the outer end of the barrel 21 is secured. At the outer end of the tubular member 15 the burner barrel 21 is slidably supported by part of a support bracket 25, which bracket is secured to the tubular member 15 and carries a pneumatic cylinder (not shown) of piston and cylinder means for moving the burner tail piece 24, and therewith the burner barrel 21 and the atomizer head 23, longitudinally of the tubular member 15. The support bracket 25 also carries an oil valve box 26 to which oil for the oil burner is supplied and from which an oil hose (not shown) leads to the burner head.

The support bracket 25 also carries a pneumatic cylinder (not shown) of piston and cylinder means for moving longitudinally an igniter tube (not shown) also extending within the tubular member 15 and arranged to one side of the burner barrel 21 and carrying at its inner end an electric spark igniter tip.

When the burner tail piece, burner barrel and burner atomizer head are projected inwardly towards the combustion chamber 5 the atomizer head attains the operative position shown in which it is within the firing port 3 and nearer the combustion chamber than the pulverized fuel burner diffuser 9, and the oil spray 27 from the atomizer head does not impinge upon the diffuser. When the burner tail piece, burner barrel and burner atomizer head are retracted outwardly away from the combustion chamber the atomizer head 23 attains an inoperative position in which it lies within the tubular member 15. When the igniter tube is in its projected operative position it lies within the firing port 3 and nearer the combustion chamber than the atomizer head 23 while it is in its retracted inoperative position it also lies within the tubular member 15.

When the pulverized coal burner 1 alone is operated and the coal flame therefrom is normal, ignition of coal particles commences within the firing port 3 at a short distance from the difluser 9 and the flame front may be at an annular surface or region roughly in the position indicated by the broken wavy line 28. When the oil burner 2 alone is operated and the oil flame therefrom is healthy, ignition of atomized oil commences within the firing port 3 at a short distance from the atomizer head 23, which is in projected position, and the flame front Will be at a line or zone roughly in the position indicated by the wavy chain line 29.

A sighting pipe 22 is provided for enabling a silicon photovoltaic cell 121 (not visible in FIG. 1 but which will be referred to in connection with FIG. 2) arranged outside the windbox 7 to view the flame fronts. The sighting pipe 22 is vertically below the pipe 6, its inner end 31 is open and is at a location below and somewhat outwardly of the difluser 9, its outer end carries a flame sighting head 33 in which the cell 121 is housed and the pipe 22 is inclined so that radiation from the flame fronts can pass outwardly along it. The flame sighting head 33 has a suitable lens 34 at its inner end and suitably the cell 121 is mounted within the flame sighting head on a printed circuit panel (not shown) located in relation to the inner face of the outer end plate 135 of the head. The said printed circuit panel in the interior of the flame sighting head also carries besides the cell 121, a transistor 120 and resistors '116 and 122 (not shown but which will be referred to in connection with FIG. 2). Referring to FIG. 2, an electric network generating output signals in dependence upon fluctuating illumination of the cell 121 includes a positive line 101, supplied through a resistor 102 from +15 volts terminal 103, stabilized in potential with respect to earth by a Zener diode 104 and connected to earth through a capacitor 105, which is connected through a resistor 106 to an amplifier 107 which is connected through a resistor 108 to a negative line 109 supplied from a l5 Volt terminal 110 and connected to earth through a capacitor 111. The amplifier comprises a p-n-p transistor 112 having its emitter connected to the resistor 106, an n-p-n transistor 113 having its emitter connected to the resistor 108, a resistor 114 connected between the collector of the transistor 112 and the base of the transistor 113 and a resistor 115 connected between the emitter of the transistor 112 and the collector of the transistor 113.

The input to the amplifier 107 is provided from the emitter, which is connected to the base of the transistor 112, of the transistor already mentioned, which is of the p-n-p type and of which the base is connected to the cathode of the silicon photovoltaic cell 121, which is of type MS4B of Ferranti Limited. The collector of the transistor 120 is connected to earth through the already mentioned resistor 122. The anode of the cell is connected to a point, connected to line 101 through a capacitor 123, between a diode 124 and a resistor 125 in a voltagedividing chain connected between the line 101 and earth and comprising, in series, a fixed resistor 126 and a variable resistor 127 connected in parallel to the line 101, the diode 124 and the resistor 125. The cell is shunted by the already mentioned resistor 116.

The collector of the transistor 113 is connected through a tapped resistor 128 to the base of a p-n-p transistor 129 of which the emitter is connected through a variable resistor 130, and, in series therewith, a resistor 131 to the positive line 101 while the collector of the transistor 129 is connected through a resistor 132 to the negative line 109. A signal S1 depending upon the flicker in the illumination of the cell is taken through a capacitor 133 from the tapping point on the resistor 128. The collector of the transistor 113 is also connected through a diode 134 other end is connected to earth and a resistor 136 of which the other end is connected to the negative line 109. The base of the transistor 129 is connected to earth through a capacitor 141. A signal S2 depending upon the average illumination of the cell 121 is taken from the emitter of the transistor 129. It is assumed that the means receiving the signal S2 provides a resistance path 142 to earth.

The point of connection between the resistors and 131 is connected through a resistor 143 to the base of an n-p-n transistor 144, of which the emitter is connected to earth while the collector is connected through a resistor 145 to the base of a p-n-p transistor 146. The emitter of the transistor 146 is connected to the positive line 101 and the collector thereof is connected through a resistor 147 and, in series therewith, a diode 148 to earth. The collector of the transistor 113 is connected with a capacitor 149 to the junction between the resistor 147 and the diode 148. The collector of the transistor 146 is connected through a resistor 150 to the base of the transistor 144. The base of the transistor 144 is also connected to earth through a diode 151.

The circuit is adapted to operate so that when the cell 121 receives normal characteristic flickering radiation from at or near the flame front of a pluverized fuel flame due to the operation of the burner 1 and/or an atomized oil flame due to the operation of the burner 2, the cell responds to generate a fluctuating E.M.F. which is amplified so that a fluctuating is produced at the collector of the transistor 113. The flicker component of this E.M.F. gives rise to the signal S1. The current through the cell is small and the said signal S1, in view of the logarithmic character of the cell response to radiation, is representative of the ratio of the flicker component of the cell radiation to the average cell radiation. By suitable choice of circuit components it is arranged that the said flicker component consists wholly or mainly of the higher frequencies characteristic of the flame front. The signal S1 is preferably passed to an amplifier the output of which is rectified to produce a signal for desired indicating and/or recording and/or controlling purposes. The capacitance 141 shunts to earth the fluctuating component of the applied to the base of the transistor 129, so that the output of the transistor 129, which is traversed by current flowing from earth through the resistor 142 to the transistor and from the transistor through the resistor 132 to the negative line 109, is a DC. signal S2 representative of the average cell radiation.

When the signal S1 denotes that the ratio of flame radiation fluctuations or flicker to average radiation at the cell has an appropriate value the flame is healthy or eflicient. If the radiation of the cell by a healthy flame changes, e.g. if it falls somewhat owing to partial interruption of the radiation path to the cell, the signal S2 will change but the signal S1 will continue to have the value denoting a healthy flame. This circumstance will be due to this, that by virtue of the logarithmic characteristic of the cell the output voltage fluctuations at the cell are not only directly proportional to the corresponding radiation fluctuations at the cell but also inversely proportional to the average radiation at the cell and both radiation fluctuations and average radiation at the cell fall proportionately if the radiation path to the cell becomes partially interrupted.

The values of the signals S1 and S2 may be displayed on the dials of indicating meters (not shown). The said meters may be mounted on a panel with a plurality of lamps of which the illuminations are arranged to denote various conditions of burner operation, for which purpose means may be provided to yield a signal indicative of the presence or absence of oil pressure at the oil burner, means may be provided to yield a signal indicative of the delivery or lack of delivery of pulverized fuel into the primary air stream therefor and the support bracket 25 (FIG. 1) may carry a housing 62 for a photo-conductive cell 63 which is arranged to receive radiation passing along the tubular member in the upper half thereof. An example of a way of labelling and controlling the illumination of such lamps is described in British Pat. No. 976,621.

The transistors 144 and 146 are normally non-conducting. The resistance value of the resistor 130 is adjusted so that when the of the signal S2 rises above a value representing a predetermined low value of cell radiation, the junction point between the resistors 130 and 131, connected through the resistor 143 to the base of the transistor 144, rises above a value enabling the transistor 144 to conduct, whereupon, by virtue of the conduction of the transistor 146 and the feed back through the resistor 150 a cumulative or trigger action takes place and the conductions of the transistors 144 and 146 rise to maxima. When the transistor 146 is conductive current flows through the diode 148, which enables the flicker component of the fluctuating at the collector of the transistor 113 to be substantially short circuited through the capacitor 149 to earth and the signal S1 is substantially annulled. Thus the circuit ceases to supply a significant signal S1 when the burner is not in operation.

The transistor 120 is a silicon junction transistor and is housed in the flame sighting head 33 together with the silicon cell 121 so that it may have the same or approximately the same ambient temperature as the cell and thereby exert a compensation for changes in the characteristic of the cell with temperature. Similarly and for a similar reason preferably the transistor 112 and the diode 124 are both silicon circuit elements and are positioned one near to the other so as to have the same or substantially the same ambient temperature.

The diode 151 is provided to make possible a current from earth through the resistor 143, when the transistors 144 and 146 are non-conducting, which will ensure suitable reduction of the voltage from the emitter to the base of the transistor 144 existing under normal circumstances.

The capacity 141 is suitably of larger value than necessary to annul the flicker component at the base of the transistor 129, so that the signal S2 is damped against immediate full responses to transient variations of average cell illumination.

The diode 134 is provided in order to ensure a certain value of the signal S2 even in the absence of cell illumination. The diode 12-4 is selected with the aim of providing compensation for the variation with temperature of the characteristics of the transistor 112. The resistance 116 is a relatively high resistance.

What is claimed is:

1. Apparatus for monitoring a flame from a burner, comprising a photovoltaic device having a logarithmic response characteristic, the device being operated such that the output thereacross is proportional to the logarithm of flame illumination thereof, an electrical circuit connected to receive the output of the device and detect variations in the E.M.F., the variations being a measure of the ratio of flame radiation flicker to average flame radiation, the electrical circuit providing an output representative of the ratio, and means connected to the output of the electrical circuit and actuatable thereby.

2. Apparatus as claimed in claim 1, wherein the photovoltaic device is a silicon photovoltaic cell.

3. Apparatus as claimed in claim 2, wherein the cathode of the cell is connected to the base of a p-n-p silicon transistor to control the current through said transistor, said transistor being positioned so as to have the same ambient temperature as the cell.

4. Apparatus as claimed in claim 3, wherein the electrical circuit comprises first and second circuit chains, the transistor is arranged to control the base current of a second silicon transistor in the first chain, the first chain is connected between a source of positive potential and a source of negative potential, the second chain is a voltage-dividing chain comprising electrical resistance in series with a silicon diode and further electrical resistance and is connected from the source of positive potential to earth, the anode of the cell is connected to the point of connection between the diode and the further electrical resistance, and the second silicon transistor and diode are positioned one near the other so as to have the same ambient temperature.

5. Apparatus as claimed in claim 4, further comprising means for annulling the output representative of said ratio when the average intensity of radiation received by the cell becomes lower than a predetermined fixed value.

6. Apparatus as claimed in claim 5, wherein the electrical circuit further comprises, a third circuit chain, a conductor carrying a fluctuating potential from the fluctuations of which the output representative of the ratio is derived, a capacitor and second diode through which the conductor is connected to earth, the second diode being in the third circuit chain, and the third circuit chain being normally non-conducting and rendered conducting by feedback means when the average intensity of radiation received by the cell becomes lower than a predetermined value.

7. Apparatus as claimed in claim 6, wherein the third circuit chain includes a normally non-conducting p-n-p transistor controlled by a normally non-conducting n-p-n transistor, the feedback means comprises a resistor connected from the base of the normally non-conducting n-p-n transistor to a point between the second diode and I capacitor and also to the collector of the normally nonconducting pn-p transistor, and the conductor is substantially short circuited to earth through the capacitor and second diode when the average intensity of radiation received by the cell becomes lower than the predetermined value.

8. Apparatus as claimed in claim 7, wherein the electrical circuit also provides an output signal representative of the average value of radiation received by the cell.

9. Apparatus as claimed in claim 2 wherein the electrical circuit has a p-n-p silicon transistor connected therein, the cathode of the cell is connected to the base of the transistor, and the transistor compensates for a change in the cells response characteristic occasioned by a change in temperature of the cell.

References Cited UNITED STATES PATENTS 2,722,677 11/1955 Krueger 340228.2 2,820,945 1/1958 Marsden 340228.2

ARCHIE R. BORCHELT, Primary Examiner M. ABRAMSON, Assistant Examiner US. Cl. X.R. 3 56223 

